Furniture having a door which rotates around a horizontal rotation axis is used, for example, in a hanging cupboard for a kitchen. A hanging cupboard for a kitchen is positioned near the ceiling, and therefore opening a door upward is convenient. A stay is interposed between a door and a main body, and supports the weight of a door that is opened to an arbitrary opening angle such that the door closes slowly.
An issue with furniture having a door that rotates around a horizontal rotation axis is that the moment of the door changes with the opening angle of the door. For example, if a door is opened upward, when the door is at the maximum opening position, the stay is subjected to a large moment from the door. On the other hand, when the door is close to the closed position, the stay is only subjected to a small moment from the door.
A typical stay is equipped with a first arm and a second arm which are connected so as to be capable of rotating around a rotation axis in two mutually opposing directions. For example, a free end of the first arm is connected to a housing, and a free end of the second arm is connected to the door. The first arm and the second arm rotate freely in one direction and rotate with a resistance force attributed to frictional force in an opposite direction. When the door is opened, the first and the second arms rotate freely with each other, and thus the door can be opened with a light force. On the other hand, when a person lets go of a door which has been opened to an arbitrary angle, the door tries to return to the closed position under its own weight. However, when the first arm and the second arm are rotated in the other direction, a frictional force works between the first arm and the second arm, and therefore the position of the door opened to an arbitrary angle can be maintained. When closing the door, the door is pushed in the closing direction, and the first arm and the second arm rotate in the other direction in opposition to the resistance force between the first arm and the second arm.
An example of this type of stay is shown in FIGS. 24A and 24B (see U.S. Pat. No. 6,584,645). This stay uses a combination of a friction element and a wedge element, and is provided with a first arm 1, a second arm 2, a disk 3 housed in a ring-shaped crown 2a of the second arm 2 so as to be capable of rotating around a rotation axis, an elastic member 4 which presses the first arm 1 to the disk 3, and rollers 5 interposed between a first opposing surface 3a of the disk 3 and a second opposing surface 2a1 of the crown 2a of the second arm 2. A width of a gap between the first opposing surface 3a and the second opposing surface 2a1 gradually narrows in a clockwise direction (1).
When the second arm 2 rotates in a counterclockwise direction (2), the rollers 5 move to a gap that is wider between the first opposing surface 3a and the second opposing surface 2a1. Therefore, the torque of the second arm 2 is not transmitted to the first arm 1, and the second arm 2 rotates freely in the counterclockwise direction (2) with respect to the first arm 1. On the other hand, when the second arm 2 rotates in the clockwise direction (1), the rollers 5 move to the gap that is narrower between the first opposing surface 3a and the second opposing surface 2a1, and become stuck therebetween. Therefore, the torque of the second arm 2 is transmitted to the first arm 1. When the torque acting on the second arm 2 is larger than the frictional force between the disk 3 and the first arm 1, the disk 3 slides with respect to the first arm 1. Accordingly, the second arm 2 rotates with resistance force in the counterclockwise direction (2) with respect to the first arm 1.